Technique for filling reclamation of mining subsidence land with Yellow River sediment

Abstract: Mining subsidence is one of the most prominent environmental problems in the plain area with high groundwater level in Eastern China. The recovery percentage of cultivated land with non-filling reclamation techniques, such as "Digging deep to fill shallow", "Directly reconditioning" and "Drainage" is too low, while filling reclamation technique is an effective way to solve the problem. However, the filling reclamation material, such as coal gangue and fly ash, has disadvantages of limited amount and potential contamination. Other filling material such as lake mud can only be used in mining areas close to the lake, and the thick mud layer of the reclaimed land needs about 3 years to drain away the water, which is a very long time for land reclamation. Thus new land reclamation techniques need to be explored. In this study, a new technique of filling reclamation of mining subsidence land with Yellow River sediment was implemented in an experimental site in the north of Jining City, and the technique process, reclaimed landscape and soil profiles, soil physical and chemical properties, and reclaimed farmland productivity were introduced. The results indicated that 100 percent of land could be reclaimed with the new technique, in which more than 95 percent could be reclaimed to cultivated land. The reclaimed farmland had comparable landscape with that of the control farmland, proving that the new technique was feasible. However, there were some deficiencies of the capacity to retain water and fertility for the reclaimed soil profiles. The water contents of the surface soil layer (0-20 cm), subsoil layer (＞20-50 cm) and substratum (＞50-80 cm) of the reclaimed farmland were 9.16%, 5.06% and 3.67%, respectively, which were significantly lower than those of the control farmland. The pH values of the reclaimed farmland ranged from 7.5 to 8.11, which basically met the requirements of the crops in research region. The contents of total nitrogen, available potassium and organic matter of the surface soil layer (0-20 cm), subsoil layer (＞20-50 cm) and substratum (＞50-80 cm) and the content of available phosphorus of the surface soil layer (0-20 cm) of the reclaimed farmland were lower than those of the control farmland. As for the reclaimed farmland, the total nitrogen contents ranged from 0.07 to 0.53 g/kg, which were in low or very low levels according to the standard classification of the Second Soil Survey of China. The available phosphorus contents ranged from 4.46 to 7.73 mg/kg and were in low or medium levels. The available potassium contents ranged from 37.00 to 109.33 mg/kg and were in low, medium or high levels. The organic matter contents ranged from 2.66 to 11.12 g/kg, which were in very low, low or medium levels. The relatively low water and nutrient contents of the reclaimed farmland would restrict the crop growth. The field investigation showed that the reclaimed farmland had bad germination and growth of wheat seed, the plant number per square meter, grain number per plant, plant height per plant, root length per plant, dry weight per plant and thousand kernel weight were significantly lower than those of the control farmland, and the estimated wheat yield of the reclaimed farmland was only one half of that of the control farmland, indicating that the filling reclamation process needed to be innovated and the reclaimed soil needed to be improved. On the basis of the analysis of technical feasibility, the following studies should be conducted in the future, such as the innovation of the reclaimed soil profile reconstruction, innovation of filling reclamation process with fast drainage, design or innovation of highly efficient dredging equipments and optimal technical parameters of sediment transportation by pipeline in long distance. When the new technique of filling reclamation of mining subsidence land with Yellow River sediment in long distance is successfully developed, it can be popularized and applied in many coal mining areas close to Yellow River in Henan and Shandong Provinces in the future.